Generally, a rotating electrical machine for vehicle is provided in an engine room. Therefore, the rotating electrical machine for vehicle in use has an extremely high temperature. The internal temperature of the rotating electrical machine for vehicle further increases due to heat generated when the rotating electrical machine for vehicle performs an operation such as power generation or driving. Therefore, when the temperature of the rotating electrical machine for vehicle excessively increases due to continuous operation for a long time, failure due to breakage of internal components may occur in the rotating electrical machine for vehicle.
Considering the above, in a conventional output control method or output control device for an AC power generator for vehicle, as means for preventing failure of the AC power generator for vehicle due to temperature increase, a method is proposed in which the temperature of the AC power generator or the ambient temperature is measured, and when it is detected that the temperature exceeds a predetermined abnormal temperature value, AC power generator output current is limited to reduce thermal load on a control device (for example, see Patent Document 1).
However, the output control method and the output control device of the AC power generator for vehicle described in Patent Document 1 detect the temperature of the AC power generator for vehicle by a temperature sensor and limit field current, thereby protecting the AC power generator for vehicle from temperature increase. Therefore, it is necessary to provide a temperature sensor, thus causing a problem that the cost of the AC power generator for vehicle increases and the configuration thereof needs to be changed.
Considering the above, in Patent Document 2, if field current flowing in a field winding has continued to be equal to or greater than a predetermined threshold value during a predetermined time, the applied field current is limited within a range that does not cause breakage due to heat generation, thus preventing excessive temperature increase.